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The Basics Of Plant Lighting (Part2)

Which Lighting system to use?
Each grow room and grower is different. The wants, needs, and requirements for your grow room will be different. The first thing we need to think about is what kind of light we are going to use. There are a few things we need to cover before we get in to lighting systems. The first is color temperature. Kelvin (K) is the standard rating system for point source white lighting. The sun has a color corrected temperature of ~6500K on a normal overcast day and ~ 22,000k on a completely clear day. This number varies greatly depending on a number of things like: cloud cover, latitude, humidity, and other atmospheric conditions. The more blue the hue of the light the Higher the color temperature will be. Likewise, the more red hue it has the lower the color temperature. This rating type works well for most single point light sources, however, it does not work for single color LED lights.

Now let’s get down to the information that everyone really wants. What type of lighting should I use? How much should I use? How far away should my lights be?
The type of lighting you choose will be based on the area you need to cover, the amount of ventilation you have available, and the amount of money you want to spend.

Cost is a major factor when setting up a new grow room or expanding a current set-up. CFLs and tube fluorescents are cheap to buy and cheap to replace bulbs (which needs done every 4-6 months). HPS and MH systems can cost quite a bit more to purchase starting at around $200. The bulbs can be pricy as well costing up to $60 or more each. LEDs are by far the most expensive. Panels can cost as much as $3 to $4 per watt (and more for some companies). However, the “bulbs” last for as much as 5 years without any noticeable degradation. The “driver” or power supply (called ballast for HID lighting) will be the first thing to fail with an LED system. If you are considering LEDs, make sure the company has a good service/repair policy.
Remember that heat and ventilation will play a role in this selection as well. If you do not have any venting available for your room, HPS/MH lighting is NOT for you. Likewise, if you have heat problems in your grow area you will want to avoid HPS/MH lighting as well.


How much light should I use?
The following is a MINIMUM light requirement for productive growth in the vegetative stage:
CFL: 42.25 watts per square foot
HPS/MH: 32.5 watts per square foot
LED: 22.75 watts per square foot

The following is a MINIMUM light requirement for productive growth in the flowering stage:
CFL: 65 watts per square foot
HPS/MH: 50 watts per square foot
LED: 35 watts per square foot